It has been widely known that when a passage through which a liquid, such as water or the like, passes is abruptly closed there occurs the so-called water hammer with which the pressure rises inside the passage on the upstream side of the closed point in a vibratory manner, thereby causing various problems such as the breakdown of devices or instruments connected to the passage due to the water hammer.
Thus, various techniques have been developed to prevent the occurrence of a water hammer. However, these techniques basically employ either one of the following methods, that is: (1) the time for closing a fluid passage is set to be slightly longer, or (2) the vibrating pressure generated inside of the passage is released to the outside by opening a bypass passage, or is absorbed by a separately installed accumulator. The former method is found to be time-consuming for closing the fluid passage, thus resulting in failure to meet the need for prompt closing of the passage, while according to the latter method, the added costs for the bypass passage or the accumulator attachments is too high.
The afore-mentioned issues regarding the water hammer effect have been discussed in those industrial fields where fluid involves a relatively large flow quantity. In recent years, however, in fields where a small flow quantity is involved, for example, in a field where wafer cleaning in semiconductor manufacturing or chemical products manufacturing are encountered, it has become very important to prevent the occurrence of a water hammer at the time of urgent closure of supplied fluid in order to improve maintenance of facilities, improve product quality, and, further, achieve upgrading of so-called throughput characteristics in the manufacturing process.
Patent Document 1: Toku-Kai-Hei No. 7-190235 Public Bulletin
Patent Document 2: Toku-Kai No. 2000-10602 Public Bulletin
Patent Document 3: Toku-Kai No. 2002-295705 Public Bulletin
On the other hand, the inventors of the present invention have developed and disclosed techniques to solve the afore-mentioned problems related to conventional techniques for preventing the occurrence of the water hammer effect, namely, (1) not being able to cope fully with urgent passage closure without basically setting a slightly longer a closing time of the fluid passage, and (2) not being able to cope fully with the rising facilities' costs incurred by adding measures that basically absorb or release the vibrating pressure. Thus, the present invention makes it possible to abruptly close a fluid passage quickly and surely at low cost and without generating a water hammer. In particular, the techniques of the present invention allow a fluid passage to be abruptly closed without the occurrence of a water hammer and, in an extremely short lapse of time (for example, within 1000 msec), by performing closure of a valve provided on the fluid passage by means of multi-step closing operations. Also, the techniques of the present invention determine the conditions for closing the valve in advance of actual closure, and in order to make it possible for the fluid passage to close without a water hammer forming, by actually conducting valve closing tests so that the actuator of the valve body is operated by an electro-pneumatic conversion device in which valve closing conditions are stored. Thus, water hammerless closing of the fluid passage is achieved quickly and surely.